Polishing compositions and use thereof

ABSTRACT

Slurry compositions comprising abrasive particles and solid lubricant particles are useful for planarizing surfaces, and preventing delamination and scratches.

TECHNICAL FIELD

[0001] The present invention relates to slurry compositions. The slurrycompositions are useful for polishing and especially for planarizingsurfaces in the microelectronics industry. More particularly the presentinvention relates to increasing the topological selectivity ofplanarizing compositions by employing slurry compositions containingsolid lubricant particles. An added advantage of such slurrycompositions is that the reduced friction reduces delamination (peeling)due to polishing, which is particularly important in polishing low k andporous low k dielectrics, and reduces defects such as scratches.

BACKGROUND OF THE INVENTION

[0002] In the fabrication of microelectronics components, a number ofsteps involved are polishing, especially surfaces forchemical-mechanical polishing for the purpose of recovering a selectedmaterial and/or planarizing the structure. Accordingly, over the years,a number of vastly different types of polishing processes to removematerial, sometimes in selective areas, have been developed and areutilized to varying degrees.

[0003] For instance, in microelectronics planarization metal orinsulator layers are deposited conformably into etched trenches of asubstrate after which a need exists to planarize the surface withchemical mechanical planarization (CMP). With device dimensions becomingsmaller and smaller involving not only narrower lines but also thinnerlayers both in front-end, and back-end of the line applications, postCMP specifications for permissible deviation from perfect planarity arebecoming tighter. The deviation from perfect planarity, referred to as astep, is detrimental due to depth-of-focus issues in subsequentlithography steps. Also, this deviation in the case of oxide polish canlead to field threshold problems in isolation regions, while in the caseof metal polish can cause shorts in the next metal level. For devicesmanufactured in the near future it is important to achieve apost-planarization step-height of less than 100 Angstroms on a 100microns×100 microns test site. Another important issue is surfacedamage, such as, peeling and scratches, particularly in polishing low kand porous low k dielectrics.

SUMMARY OF THE INVENTION

[0004] The present invention provides for improving the topologicalselectivity of the polishing by including solid lubricant particles inthe polishing composition. This is achievable by the present inventionin a single step CMP process without the need for any auxiliary processsteps or auxiliary filling structures.

[0005] More particularly, an aspect of the present invention relates toa polish composition comprising abrasive particles and about 0.03% toabout 10% by weight of solid lubricant particles.

[0006] Another aspect of the present invention relates to a method forpolishing a surface by providing on the surface a liquid slurrycomposition comprising abrasive particles and solid lubricant particlesin an amount sufficient to increase the topological selectivity of thecomposition when contacting the surface with a polishing pad; andcontacting the surface with a polishing pad.

[0007] A still further aspect of the present invention relates to amethod for polishing a surface by providing on the surface a liquidslurry composition comprising solid lubricant particles in an amountsufficient to reduce scratching and/or delamination when polishing thinfilms; and polishing said surface. The thin films are typically 2 μm orless.

[0008] Other objects and advantages of the present invention will becomereadily apparent by those skilled in the art from the following detaileddescription, wherein it is shown and described preferred embodiments ofthe invention, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects,without departing from the invention. Accordingly, the description is tobe regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 a illustrates a structure before planarization.

[0010]FIG. 1b illustrates a structure after “perfect” planarization.

[0011]FIG. 1b′ illustrates a structure with dishing due to theplanarization.

[0012]FIG. 2 illustrates a parallel plate arrangement for rheologicaltesting.

[0013]FIG. 3 is a graph showing torque and second order normal force asa function of time in a dry condition.

[0014]FIG. 4 illustrates the second order normal force as a function ofthe square of the torque in the dry condition.

[0015]FIG. 5 shows the second order normal force as a function of thesquare of the torque using a ceria slurry and a composition of thepresent invention.

[0016]FIG. 6 shows a patterned surface having up and down area duringplanarization when a).the pad does not touch and b). when it does touchthe bottom surface of the down area. Wafers are upside down duringplanarization.

[0017]FIG. 7 shows the cumulative polish rate of down area as a functionof step-height using a ceria slurry.

[0018]FIG. 8 illustrates the cumulative polish rate of down area as afunction of step-height using a composition of the present invention.

[0019]FIG. 9 illustrates post CMP dishing on a 100 μm×100 μm teststructure.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

[0020] According to the present invention a polishing slurry thatcontains abrasive particles and solid lubricant particles is provided.The solid lubricant particles enhance the topological selectivity of thepolishing. In addition, by reducing the friction of the polishingprocess it reduces the occurrence of thin film delamination andscratching.

[0021] Examples of suitable solid lubricant particles are inorganicmaterials such as molybdenum disulfide, molybdenum diselenide, tungstendisulfide, tungsten diselenide, niobium disulfide, niobium diselenide,graphite, and organic polymers such as poly (tetrafluoroethylene)(PTFE); fluoroethylene-propylene copolymers (FEP), perfluoro-alkoxyresins (PFA) and polyvinylidene fluoride (PVDF).

[0022] The preferred lubricants are the organic materials and the mostpreferred are virgin polytetrafluoroethylene particles.Polytetrafluoroethylene is preferred because of its very low coefficientof friction (0.03-0.1) and its chemical inertness.

[0023] The inorganic lubricants are not especially preferred sincecertain of them such as the disulfides and disilenides may formcorrosive acids by hydrolysis, and graphite may promote corrosion bygalvanic action.

[0024] The lubricant particles typically have a function coefficient ofless than about 0.3 and more typically about 0.03 to about 0.1.

[0025] The particle size of the lubricant particles is typically about0.05 to about 18 microns and more typically about 0.05 to about 0.5micron. A typical average particle size is about 0.2 micron.

[0026] The preferred organic polymers typically have weight averagemolecular weights about 1×10⁵ to about 5×10⁵, and more typically about2×10⁵ to about 3×10⁵.

[0027] Aqueous dispersions of PTFE particles in water stabilized bywetting agents are commercially available. They contain 3-6 weightpercent of a nonionic or anionic wetting agent or dispersant(stabilizer). By way of example, in the present application, FLUOTRON110 from Carroll Scientific was used, which has 0.2 μm average virginPTFE particle size at a pH of 7.5. Another example is Dupont PTFE FPD3584 having an average particle size of 0.2 μm at a pH of 10.

[0028] The polishing compositions typically contain about 0.03 to about10% by weight, more typically about 0.5 to about 5% by weight andpreferably about 1 to about 3% by weight of the lubricant particles.

[0029] The compositions can also contain a surfactant to keep thelubricant particles suspended in the composition.

[0030] The surfactant, when present, is typically anionic or nonionic.Specific examples of suitable surfactants can be determined by those ofordinary skill in the art once aware of this disclosure and need not bediscussed to any further extent in this application.

[0031] The amount of surfactant, when present, is typically about 3 toabout 6% by weight of the lubricant particles.

[0032] Examples of suitable abrasive particles include alumina, ceria,silica, titania, zirconia, polymer particles, organic/inorganiccomposite particles or combinations thereof. The abrasives typicallyhave a particle size of about 30 to about 1000 nanometers and preferablyabout 75 to about 300 nanometers.

[0033] The amount of abrasive particles is typically about 0.1 to about20 percent by weight and more typically about 0.3 to about 2 percent ofweight.

[0034] The slurry can include other ingredients in addition to theabrasive, solid lubricant particles and surfactants such as oxidizingagents, preservatives, anticorrosion agents and the like.

[0035] The slurry is preferably a aqueous slurry, though non-water-basedslurries or a mixture of water based and non-water-based slurries areincluded in the present invention.

[0036] The parameters of the polishing or planarizing can be determinedby those skilled in the art, once aware of this disclosure, withoutexercising undue experimentation. For instance, the speed of rotation ofthe polishing pads and also of the wafer is about 10 to about 150 rpmand pressure about 2 to 10 psi. A wafer may be in the range of 100 to300 mm in diameter.

[0037] To facilitate a further understanding of the present invention,reference is made to the figures. For an example, a shallow trenchisolation (STI) structure is shown in FIG. 1a before planarization. Inorder to achieve perfect planarization, a CMP process is required whichhas a high degree of topological selectivity meaning that it removesmaterial from the “up” areas on the wafer, but it does not removematerial from the “down” areas of the wafer until the level of the uparea reaches the level of the down area as shown in FIG. 1b. If materialis removed from the down area before it becomes level with the up area,“dishing” results i.e. a post CMP step will remain as shown in FIG. 1b′.With a large overfill, where overfill is film thickness minus stepheight, the dishing may be reduced provided the cumulative removal ratein the down area for the overfill equals the cumulative removal rate ofthe total film in the up area.

[0038] In order to achieve a perfect topological selectivity, it wouldbe desirable to understand the mechanism by which the down areapolishes. It is well known that significant polish rates result only incases where the polishing pad is in contact with the wafer.Understanding the mechanism by which the polishing pad extends in thedown area of the wafer would therefore be desirable. Accordingly,rheological experiments were made in the parallel plate configurationpresented in FIG. 2. The two parallel plates are 25 mm in diameter. A2.5 mm diameter disk was cut out from the most commonly used polishingpad, IC1000 K-GR, a foam polyurethane pad from Rodel corporation, whichis 1.34 mm thick and has adhesive backing. This was attached to thebottom plate, while a 28 mm diameter patterned silicon wafer with anSiO₂ film on it was bonded to the top plate. Axial loads of variousmagnitudes were applied in the different tests. The bottom plate wasrotated in contact with the stationary wafer. Shear rate was varied byvarying the revolution of the bottom plate. Shear rate depends linearlyon the rate of rotation times the radius of the pad and inversely on padthickness. The torque between the pad and the wafer was varied by eithervarying the shear rate or varying the down force P. The torque betweenthe pad and the wafer is the indicator of the friction created betweenthe pad and the wafer.

[0039]FIG. 3 shows the torque as a function of time in the case the padand wafer are rubbed against each other in the dry condition. An axialload of 1280 g was applied while the shear rate was 600 reciprocalseconds. It is seen that the average value of the torque between 9 and10 seconds went up to 567 g-cm. This torque created a second ordertensile normal force in the polyurethane pad. If this tensile normalforce is not counteracted by increasing the compressive force that wasapplied initially, the pad would extend in the vertical direction. Sincethe experiments were run in a mode which keeps the gap (pad thickness)between the parallel plates constant, an additional 370 g compressivenormal force was applied by the rheometer that was necessary to preventthe pad from extending in the vertical direction. This additional normalforce is also shown in FIG. 3. The tensile normal force created in thepad by the torque is a second order effect and therefore it depends onthe square of the torque. See Freudenthal and Ronay, Proc. Roy. Soc.A292, 14 (1966).

[0040]FIG. 4 shows that whether the torque was increased by increasingthe initial down force or by increasing the shear rate, the second ordernormal force is a linear function of the square of the torque with aslope of 1×10⁻³ g/(g.cm)² in the dry condition.

[0041] Next the pad was wetted with 3 drops of an aqueous ceria slurryconsisting of 0.75 wt. % ceria particles of 0.27 micron average diameterat a neutral pH.

[0042] Several experiments were carried out using always a new pad and anew wafer, the torque and the normal force were measured. The resultsare presented in FIG. 5. It is seen that the second order normal forcecreated by the torque between the pad and the wafer is larger than itwas in the dry condition. FIG. 5 shows that the normal force is again alinear function of the square of the torque as it was in the drycondition, but the slope is larger, 2.7×10⁻³ g/(g.cm)² as compared to1×10⁻³ g/(g.cm)². The rheology measurements are giving the second ordertensile normal force, which, of course, is causing a second ordertensile extension of the pad. This, however, cannot be measured with therheology test; therefore they were estimated with carefully plannedpolishing experiments.

[0043] In order to estimate the magnitude of the second order extensionof the pad in the vertical direction, perpendicular to the plane of thepad and into the down areas of the wafer, polishing experiments on aWestech 372 polishing tool using the same pad, the same slurry and thesame wafer structure—but in a 200 mm diameter size—as they were used inthe rheology tests were conducted. 350 g/cm down force and 100 rpmrevolution of the polishing table and 100 rpm revolution on the wafercarrier was used. Polishing several wafers for different times it wasrecommended that the cumulative polishing rate in the down area of a 100micron×100 micron test structure as a function of step-height wasdetermined. The oxide thickness in the down area was measured with a TF1thin film optical spectrometer by Tencor and step-height with a P-11Profilometer of KLA Tencor. The polishing rate is assumed to be slowwhen the pad does not touch the down area representing hydrodynamicconditions (FIG. 6a) and fast when it does (FIG. 6b). In FIG. 7 thecumulative polish rate of the down area as a function of step-heightusing the 0.75 wt. % ceria slurry is shown. A transition from a slow toa fast polishing rate occurs at about 1700 Angstroms step-height, fromwhich it is concluded that the pad extended into the down area by thesecond order extension by about 1700 Angstroms.

[0044] According to the present invention, the second order normal forceand the accompanying second order extension of the polishing pad intothe down areas of the wafer is reduced. As seen in FIG. 5 normal forceis a very sensitive function of the torque, thus the way to reduce thenormal force is to reduce the torque i.e. to reduce the friction betweenpolishing pad and wafer. .

[0045] A slurry is prepared by diluting a commercially available aqueousPTFE suspension, FLUOTRON 110 from Carroll Scientific, Inc., undervigorous stirring to a concentration that gave 3.0 wt. % in the finishedslurry. The PTFE particles were 0.2 micron in diameter, have a molecularweight of 2×10⁵ to 3×10⁵ and were stabilized with an anionic surfactant.The suspension had a neutral pH. Subsequently added under continuousstirring to the PTFE suspension is in an aqueous ceria slurry in anamount that gave a ceria concentration of 0.75 wt % in the finishedslurry. The pH of this slurry remained neutral.

[0046] Rheological experiments were conducted while wetting thepolishing pad with 3 drops of the slurry. In the experiments a shearrate of 500 reciprocal seconds and an initial down force of 1240-1266 gwas applied. The torque measured between 9 and 10 seconds was in everycase less than 200 g.cm indicating that the addition of 3 wt. % PTFEsignificantly reduced the torque as compared to the torque createdwithout the PTFE additive.

[0047] The second order normal force was a maximum of 4 g, and in someexperiments totally absent (−13 g). The torque and normal force valuesare also plotted in FIG. 5.

[0048] The results of polishing experiments using the 0.75 wt.5% ceriaand 3.0 wt. % PTFE slurry are shown in FIG. 8, presenting the cumulativeremoval rate of the down area in the test site as a function ofstep-height. The results show a steady polish rate at every step-heightwith possibly a small increase in removal rate at 100 Angstromsstep-height, though the rates are within the experimental scatter. Theseresults should be compared with that of FIG. 7. While there the padextended to 1700 Angstroms into the down area of the wafer, when thePTFE additive was used, the pad did not extend into the down area of thewafer, or if it did, it was just with 100 Angstroms implying that in thepresence of PTFE particles in the slurry no second order extension wascreated in the pad. Post CMP measurements on the 100 micron×100 microntest site showed a dishing of less than 100 Angstroms deep. FIG. 9 showsa post CMP dishing of 40 Angstroms on a 100 micron×100 micron test siteon a wafer that had initially a 3600 angstroms step height and 4900angstroms high density plasma SiO₂ film on it, thus a 1300 angstromsoverfill. Such overfill is necessary because the removal rate in thedown area under hydrodynamic conditions increased from the PTFEparticles.

[0049] The polishing results together with the rheological measurementsshow that adding 3 wt. % PTFE particles to the polishing slurry reducesfriction as indicated by a reduced torque and prevents the creation ofsecond order normal force and second order normal extension in thepolishing pad, which enhances topological selectivity and thusdiminishes post CMP dishing. In further experiments a ceria slurry with2 wt. % PTFE additive was prepared and the topological selectivity wassimilar to that achieved with 3 wt. % PTFE additive. A 1 wt. % PTFEadditive produced a better planarization than prior art planarizingslurries, but not as high topological selectivity as slurries with 2 wt.% and 3 wt. % PTFE additive.

[0050] Because planarizing processes utilize friction, reducing frictionby adding a lubricant to the slurry may reduce the polish rate. Thepolish rate for High Density Plasma SiO2 under the given experimentalconditions was 2000 Angstroms per minute for the 0.75 wt. % ceriaslurry, 2200 Angstrom per minute for 0.75 wt. % ceria and 1 wt. % PTFEslurry and 1250 Angstrom per minute for the 0.75 wt. % ceria and 3.0 wt.% PTFE slurry, the later still being an economical planarizing rate forthe thin oxide layers that have to be removed in future devices.

[0051] The solid lubricant particles do not adversely interfere with thepolishing process. While the examples described above are for SiO₂, thepresent invention is applicable to all CMP processes to polishingmetals, such as copper, tungsten, etc. and; insulators, such as SiO₂,low k dielectrics and porous low k dielectrics. The reduction offriction of the polishing process by the solid lubricant particles inthe slurry is particularly favorable in the case of low k dielectricswhere integration schemes are limited by delamination caused by thefriction of CMP processes.

[0052] The foregoing description of the invention illustrates anddescribes the present invention. Additionally, the disclosure shows anddescribes only the preferred embodiments of the invention but, asmentioned above, it is to be understood that the invention is capable ofuse in various other combinations, modifications, and environments andis capable of changes or modifications within the scope of the inventiveconcept as expressed herein, commensurate with the above teachingsand/or the skill or knowledge of the relevant art. The embodimentsdescribed hereinabove are further intended to explain best modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other, embodiments and with thevarious modifications required by the particular applications or uses ofthe invention. Accordingly, the description is not intended to limit theinvention to the form disclosed herein. Also, it is intended that theappended claims be construed to include alternative embodiments.

What is claimed as new and desired to be protected by letters patent ofthe United States is:
 1. A method for planarizing a surface which isformed on a substrate which comprises providing on the surface to beplanarized a liquid slurry composition comprising abrasive particles andsolid lubricant particles; and contacting said surface with a polishingpad.
 2. The method of claim 1 wherein the amount of the solid lubricantparticles is about 0.3 to about 10% by weight.
 3. The method of claim 1wherein the lubricant particles are selected from the group consistingof molybdenum disulfide, molybdenum diselenide, tungsten disulfide,tungsten diselenide, niobium disulfide, niobium diselenide, graphite,poly (tetrafluoroethylene), fluoroethylene-propylene copolymers,perfluoroalkoxy resins, polyvinylidene fluoride and mixtures thereof. 4.The method of claim 1 wherein the lubricant particles have a coefficientof friction of 0.03 to about 0.3.
 5. The method of claim 1 wherein thelubricant particles have a particle size of 0.05 to about 18 microns. 6.The method of claim 1 wherein the abrasive particles comprise a memberselected from the group consisting of ceria, alumina, silica, titania,zirconia, polymer particles, organic/inorganic composite particles, andcombinations.
 7. The method of claim 1 wherein the amount of theabrasive particles is about 0.1 to about 20 percent by weight.
 8. Themethod of claim 1 being an aqueous slurry.
 9. The method of claim 1wherein the composition further comprising a surfactant.
 10. A slurrycomposition comprising abrasive particles and solid lubricant particles.11. The composition of claim 10 wherein the amount of the solidlubricant particles is about 0.03 to about 10% by weight.
 12. The methodof claim 10 wherein the lubricant particles are selected from the groupconsisting of molybdenum disulfide, molybdenum diselenide, tungstendisulfide, tungsten diselenide, niobium disulfide, niobium diselenide,graphite, poly (tetrafluoroethylene), fluoroethylene-propylenecopolymers, perfluoroalkoxy resins, polyvinylidene fluoride and mixturesthereof.
 13. The composition of claim 10 wherein the lubricant particleshave a coefficient of friction of 0.03 to about 0.3.
 14. The compositionof claim 10 wherein the lubricant particles have a particle size of 0.05to about 18 microns.
 15. The composition of claim 1 wherein the abrasiveparticles comprise a member selected from the group consisting of ceria,alumina, silica, titania, zirconia, polymer particles, organic/inorganiccomposite particles and combinations thereof.
 16. The composition ofclaim 10 wherein the amount of the abrasive particles is about 0.1 toabout 20 percent by weight.
 17. The composition of claim 10 being anaqueous slurry.
 18. The composition of claim 1 which further comprises asurfactant.
 19. The composition of claim 1 which further comprises atleast member selected from the group consisting of oxidants,preservatives and anticorrosion agents.
 20. A method for planarizing asurface which is formed on a substrate which comprises providing on thesurface to planarized a liquid composition comprising abrasive particlesand solid lubricant particles; and contacting said surface with apolishing pad.
 21. The method of claim 20 wherein the surface to bepolished is a thin film.